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Microwave method for graphene quality control

Research into graphene, the wonder material of the last decade is now maturing into providing the quality control methods and processes which will lead to impact on UK industry.

As usual, in disruptive technology developments, the material applications are expected to develop from research through measurement and standards to real widespread industrial uses.

The recent invited paper published in IET journal Circuits Device and Systems illustrates how the measurement community is gearing up to provide the capability to monitor the electrical properties of graphene during large scale production, without the need for any contact to the ultra-thin material. The image shows the NPL non-contacting microwave system used for quality control, as demonstrated in recent field trials. This can be an extremely rapid process, ideally suited for on-line growth and production for quality control used in industry. This is important in the scale up from laboratory to factory to enable industry to have confidence in graphene product quality.

Fig 1: (a) Plot of the Lorentzian lineshape of the TE010 resonance of the sapphire puck shows a set of VNA traces for the three stages of the measurement process. Curve A (blue) shows the high Q Lorentzian lineshape observed for the resonator with no substrate. Note that the linewidth is around 1 MHz. The second curve B (pink) is shifted down in frequency by the presence of a bare quartz substrate but the Q value is essentially unchanged since the quartz substrate has a very low loss tangent. The third curve (C) with an identical quartz substrate coated with CVD graphene shows a much reduced Q value though the frequency is only slightly shifted from that of the bare substrate. (b) Image of the NPL microwave system.